Current civil aircraft make widespread use of digital technologies. Various devices comprising an electronic communication interface, such as processors or other devices equipped with microprocessors or microcontrollers, ensure functions of command, control and surveillance on board aircraft. These devices exchange information, or data, by means of digital buses.
The buses used most are electrical buses. These electrical buses comprise cables having a metal conductor core, generally made from copper or aluminum. The digital data are then sent in the form of electrical voltage changes. The technology of the electrical buses, in particular the serial bus where the coded information is sent successively on the same physical medium, is justified in particular by the reliability of the means of connection which are, on board aircraft, subjected to severe operational environments. However, these electrical buses have the drawback of being relatively heavy and of being sensitive to electromagnetic disturbances.
The need, especially for operational reasons of interchangeability, a high level of stability in the specifications of the devices utilized on board aircraft, in particular with respect to their physical and functional interfaces, has led aircraft manufacturers to standardize the mechanical and electrical interfaces of these devices.
Standard ARINC 429, which defines, in detail, the communication protocols and interfaces between the devices on board aircraft by means of one-way buses that meet this standard, is well known to the aeronautical world, for instance.
More recently, simplifying electrical buses has been made possible by the increase in speeds that these buses are now able to support, with the reliability conditions necessary for aeronautical applications. In this way, several relatively low-speed one-way buses used in systems complying with standard ARINC 429 can be replaced by one high-speed two-way bus, for example 100 Megabits per second. These high-speed two-way buses are associated with new standards and, as a result, new communication interfaces for the avionics devices.
Currently, these new interfaces are always associated to electrical communication buses, for the reasons of operational reliability already mentioned.
FIG. 1 shows an architecture example of on-board electronic devices, linked by high-speed electrical buses. In this example, processors 1a, 1b, 1c are linked by electrical communication buses, 4a, 4b, 4c respectively, to a commutator 2. This commutator 2 is a standard device able to make the signals pass from one bus to another bus, depending on address signals that arrive over the bus itself. Other devices 3a, 3b, for example sensors or actuators, are linked directly to the processors, 1a, 1b respectively, by means of electrical communication buses, 5a, 5b respectively.
The simultaneous two-way electrical communication buses, called Full-Duplex buses, are generally constituted of two pairs of electrical conductors, or cables (called quadraxial), each pair being dedicated to one communication direction. In general, each pair is twisted. A bus thus constituted comprises a shielding intended, on the one hand, to protect the cables from electromagnetic attacks from the exterior and, on the other hand, to protect the exterior environment from electromagnetic rays that may be emitted by the cables.
These cables frequently have a mass per unit length of 40 to 50 g/m.
Each bus is equipped, at each of its ends, with a connector, male or female as needed, comprising four electrical contacts and having a shielding connection on the metal structure of said connector. Standard ARINC 600 describes the electrical and mechanical characteristics of such a quadraxial type of connector. In such a connector with 4 electrical contacts, the two contacts dedicated to transmission are generally identified as Tx+ and Tx− and the two contacts dedicated to reception are generally identified as Rx+ and Rx−. The + and − signs of these identifications indicate that the bus is polarized and this polarity must be respected when the connectors are fitted on the electrical cable of the bus.
In recent years, optical means of sending information have been developed. The information to be sent is converted into optical signals that can be propagated in optical fibers. The communication buses sending such optical signals are called optical buses. They present advantages in terms of mass per unit length, speed of information and insensitivity to electromagnetic rays. However, they are still not widely used in the field of civil transport aircraft, because of problems connecting optical links onto current avionics devices. In effect, current avionics devices are equipped with interfaces for coupling electrical buses and the optical buses are equipped at their ends with optical connectors. An optical bus cannot, therefore, be connected to a current avionics device.